(1) Seven murine hybridoma monoclones (68-2-1, 57-14-2, 72-104-1, 68-3-2, 57-8-1, 10-176-1, 47-96-1) that produce antibodies specific to glutamine synthetase (GS) were established. Antibodies from these clones were purified and characterized. Two antibodies (10-76-1, 48-76-1) bind only to the monomeric form, and another two antibodies (57-14-2, 68-3-2) bind only to dodecameric GS, and the remaining three (68-2-1, 72-104-1, 57-8-1) bind to both monomer and dodecamer. None of the seven antibodies bind selectively to either Mn form or Mg form of GS. But the resulting Ab GS complexes exhibit significantly different catalytic properties depending on the divalent cation added. (2) Six murine monoclonal antibodies (37-2-1, 66-63-1, 72-76-1g 51-28-1, 96-37-17, 67-22-12) specific to either AMP or Epsilon-aza-AMP were purified. Interaction of these antibodies with GS containing various numbers of adenylylated subunits was studied by employing imunoprecipitation methods, light scattering measurement and fluorescence quenching measurement. Affinities for AMP or Epsilon-aza-AMP moieties, the rate constants for association and dissociation processes and the precipitating capability varied widely. One interesting observation we made is the unusually low rate constant for association of 67-22-12 to Epsilon-aza-AMP (9,000 1/M 1/sec. at 15 C) and to Epsilon-Aza-GS (about 64 1/M 1/sec. at 15 C). These slow rates might be due to slow conformational change(s) taking place in Ab after binding to Epsilon-aza-AMP moiety. (3) The prospect of separating the mixture of GS hybrid into uniquely adenylylated molecular entities was investigated using the immunoadsorbants prepared by cross-linking anti-AMP hybridoma proteins to Affi-Gel 10. (4) We selected a strain (JA200/pLC 18-28) which overproduces adenylyl-transferase by 10 about 20-fold from the E. coli bank of Clarke and Carbon.